When the permanent magnet motor operates, the highest temperature and the heat are mainly caused by copper loss and iron loss of the stator. Flux density in the teeth of the stator is the largest, and thus the loss is larger, causing the temperature highest at the inner surface of the stator and at the outer surface of the rotor of the motor. It is found through experiments and studies that, as the rotor is constructed by a permanent magnet, the heat caused by the rotor can be ignored. Therefore, during the operation of the motor, the rise of the temperature of the rotor is mainly caused by heat transmission. As for a permanent magnet motor, if the temperature of the rotor is too high, the motor will have hidden dangers, such as, the rotor being demagnetized, heat loss due to the insulation of the motor, and so on.
In a permanent magnet motor for a refrigeration compressor, cooling is usually done through spraying coolants or providing a spiral flow channel between the stator and the case. In practical applications, these manners of cooling have following problems: the effect of cooling the rotor of the motor is poor; the thermal field inside the motor is not uniform, that is, the temperature is too high at some regions but is too low at some other regions.